The prior art is replete with apparatus for applying rolled sheet material to a surface. The art is also replete with apparatus for welding or bonding thermoplastic sheets together and along their overlapping edges. For example, U.S. Pat. No. 4,806,194 to Wald and U.S. Pat. No. 4,354,893 to Kugler, et al. disclose apparatus for heating and applying rolled sheet material to a surface such as a roof. Russian Patent Nos. 473,786 and 1,375,764 also disclose apparatus for heating and applying sheet material to a surface such as a roof. U.S. Pat. No. 4,460,433 to Boyd discloses non-heating apparatus using a pressure roller to apply or press thermoplastic sheet to a surface. The outer shell of the pressure roller in Boyd is constructed out of a flexible material which deforms in a direction perpendicular to the roof but not in any other direction to apply uniform pressure on the sheet. U.S. Pat. No. 4,913,772 to Taylor, et al. discloses an apparatus for welding a strip over abutting or overlapping edges of individual thermoplastic sheets to seal the sheets together. The machine uses both heat and pressure to weld the strip to the abutting or overlapping edges. U.S. Pat. No. 4,894,112 to the present inventor discloses a method and apparatus comprising a hand held device for joining or welding the overlapping edges of thermoplastic sheet material together. U.S. Pat. No. 4,872,941 also to the present inventor, discloses a self-propelled apparatus for welding thermoplastic sheets together.
While all of the above mentioned patents disclose apparatus which undoubtedly perform as intended there still remains a need for a welding apparatus which is not only capable of heating and applying a roll of sheet material to an supported surface but which is also capable of preventing the sheet material from overheating. Overheating can occur if the heating elements remain in contact with the sheet material after the operator stops applying the sheet material to the supported surface. To prevent such overheating, it is necessary to either shut off the source of heat or somehow separate the sheet material from the heating element.
A need also exists for a welding device which additionally heats the supported surface to which the sheet material is being applied so that a better bond or weld is formed between the sheet and surface.
A need further exists for a welding device as described above which is easily transported, lightweight and relatively inexpensive when compared to other commercially available welding devices.